vmkfstools is one of the ESXi Shell commands for managing VMFS volumes and virtual disks.
You can perform many storage operations using the vmkfstools command. For example, you can create and manage VMFS datastores on a physical partition, or manipulate virtual disk files, stored on VMFS or NFS datastores.

Note

After you make a change using the vmkfstools, the vSphere Client may not be updated immediately. You need to use a refresh or rescan operation from the vSphere Client.

For more information on the ESXi Shell, see Getting Started with vSphere Command-Line Interfaces.